The present invention relates to variable power optical systems.
Some zoom lens designs group the lens used in the design, with one group being used largely for zooming, a second group being used largely for keeping an image in focus, and a third group used to keep the image plane stationary. A fourth group may also be used to form a sharp image. The focusing group may be adjusted for focusing the zoom lens at any focal length position without the need to refocus for other focal lengths of the zoom lens. The zooming group (or “variator”) causes significant magnification change during zooming. The lens group that stabilizes the image plane may also be used to provide magnification.
Desirable features in a zoom lens include high zoom ratio and a wide angle field of view. As the zoom range of a lens system increases, generally the length and weight also increases. Consumer products such as cellular telephones or point-and-shoot cameras are often small and lightweight, so zoom lenses included in those products are constrained by size and weight. Moreover, as the focal length range of a lens system increases, generally focusing problems also increase usually at the wide field of view zoom positions.